I was setting up to do some studio work and the volume died after a minute or so. The valves have been making a few crackling noises and one no longer glowed so I just figured replacing that would be the thing. Swapped out the power amp valves. Both new ones glow nicely - but there is absolutely no sound at all. Swapped the fuse just in case there was an issue there (didn't seem to be but I did it anyway). Have tried different cables, speakers and speaker leads - still nothing.

Any other ideas? I have a lot of studio work coming in the next fortnight as well as a few gigs and this is the only amp I currently own.

Last time I checked the closest official repairman in Australia was 1000 km away - so can't send it there given y time restraints.

Before line6 was called line6... they used to do r&d for other companies like alesis + others. and when those customers came to visit the offices of line6 (before it was called line6) and the receptionist needed to warn all the guys who were designing products for other companies (and for themselves... ) who were like 'in the back' the receptionist would announce over a tannoy 'tellephone call for 'fred smith' on line 6' the cunning part was that they only had 5 telephone lines, so it was the secret code for "hide your sh1t the feds are comin'" or "someone's coming, let's hide these PODs that we aren't going to release for another few years so they don't see them"

I am not 100% certain as I have yet to open up my DT25 head, but the Spider Valves have a plate fuse located on the power amp PCB that requires pulling the chassis in order to change...heater fuse is also located similarly...These are in addition to the read panel protection fuse....My SV MK2 blew a power tube shortly after arriving in Atlanta from LA and it took the plate fuse with it....Anyway, the symptoms sound similar...amp fires up and the heaters glow, but no sound because the plates might not be firing up...

Thanks guys
Arislaf - not yet. I swapped them over, tried it and was going to take it to a tech/friend's place today for him to check the bias for me. If the bias was out would that actually stop it from making a sound? I didn't think it would, but happy to be wrong in this.

Bias being out of whack just might give you more xover distortion in class AB. Won't hurt anything but could compromise tone a bit. The bias adjustment has no meaning when the amp is running in class A. Did you look for an internal fuse?

your amp may be one that is covered by bulletin 59. the transformer is the subject of that bulletin. call line6 and inquire about it. certain serial numbers are affected.

I went through 3 DT-50 power transformer repairs before I got a "new" one which appears to have fixed the problem but that was only because a careless tech buggered the exterior of my amp. My casei is well documented on the forums. They are nice amps that sound really good live. Line 6 did treat me right that I cannot deny even though it was a real hassle to box up the amp and send it back each time. Call and ask for Ashley. Everyone knows her there. She is the definition of what customer service should look like. Good luck